This invention relates generally to propulsion systems for surface and subsurface vessels. More particularly, the present invention is a ribbon drive shaped as a spiral ribbon of decreasing helix angle and coil frequency within a cylinder or along the interior wall of a tubular conduit for causing water or other fluids to move with respect to the vessel when the ribbon is rotated.
Propulsion systems for marine vessels have long been the subject of various inventions. For example, U.S. Pat. No. 475,826 to Street et al. was issued for a new form of screw propeller. The propeller was enclosed in a tube and gave water entering the tube a sternward direction. In this instance, the ribbon, surrounding a central shaft, was not of uniform diameter. However, water velocity was unaffected by this invention since the frequency of the repeating curved units of the ribbon is the same along the length of the shaft.
U.S. Pat. No. 2,568,903 to Vasser was issued for a propeller construction for watercraft. This invention describes a plurality of blades inside a cylinder, the blades having an inclined helical configuration. However, the frequency of the helical inclined blades is the same over the length of the cylinder. Thus, there is no augmented, incremental acceleration of water through the structure.
U.S. Pat. No. 3,070,061 to Rightmyer was issued for a progressive thrust propeller. This invention shows a continuous vane running along the length of a shaft. However, in this instance, the frequency of the vane along the length of the shaft varies from a higher frequency in the bow direction to a lower frequency in the stern direction. Since this invention is not encased in a tube, water will be pushed sideways away from the spinning vane, thereby losing a certain amount of the potential forward thrust for the vessel.
Certain other patents simply involve propellers of various types encased in tubes. For example, U.S. Pat. No. 5,244,425 to Tasaki et al. and U.S. Pat. No. 5,324,216 to Toyohara et al. were both issued for water-jet type units, which were units with a single curve encased in tubes.
U.S. Pat. No. 5,383,802 to Nicholson was issued for a propulsion system. The system comprises a series of separate vanes on the inside periphery of a cylinder, thereby leaving a hollow central core. When the cylinder is turned, water is drawn into the cylinder and expelled in the sternward direction, thus giving a forward propulsion to the vessel. These vanes on the inside of the cylinder are, however, generally the same frequency along the length of the propulsion cylinder, and are not continuous, thus lacking the continuous application of energy transferred to water by unitary ribbon, and perhaps being likely to produce more noise as each vane cleaves the water.
While these various systems represent certain inventive approaches to propulsion of vessels, when used in submarines or torpedoes the drive systems of such vehicles is a major source of noise production. When noise is produced in an underwater environment, detection is possible. Hence, there is a premium placed upon drive systems, especially for submarines, that allow such vessels to be driven in relative secrecy and silence.
In submarine systems, the various components have been designed to operate as quietly and as vibration-free as possible. This applies to propulsion systems as well as to the systems of fans, pumps, and other mechanical and energy transfer systems that operate within the submarine hull. In addition, hull designs have been optimized for a combination of speed, maneuverability, and quietness depending on the particular intended use. For any of these uses, the power of the propulsion device is critical, and noise suppression of the propulsion device is of equal concern. Thus, there is a continuing trend and balance that must be struck to allow a submersible to move as quickly as possible with the minimum amount of noise.
What would therefore be useful is a new propulsion system for surface vessels and for submarines in particular, which allows an increased speed of the vessel, as well as a decrease in any noise created by the propulsion system when operating in a subsurface mode.
The present invention is just such a system that differs markedly from these above inventions. The present invention generally comprises a ribbon drive of progressively decreasing coil frequency and several alternative embodiments enclosed in a propulsion tube, thereby giving directed and more effective forward motion to the vessel in a fluid environment such as water, while operating quietly and efficiently with an acoustic advantage.
As will be explained in more detail below, the present invention is a ribbon drive propulsion system and method, in several different embodiments, which allows water to be moved in channels (referred to herein as a propulsion tube) inside or adjacent to a hull, in an extremely efficient and quiet manner.
It is therefore an objective of the present invention to have a surface vessel or submarine with an improved propulsion system that is both faster and quieter than other existing systems.
It is a further objective of the present invention to create a propulsion system that operates within the hull of a submarine or surface vessel, rather than outside the hull as propellers of current systems operate.
It is a further objective of the present invention to apply a novel propulsion system to both submarines and to torpedoes, and surface vessels of all types.
The ribbon drive of the present invention comprises a series of alternative embodiments, all of which share a common concept, that is, a ribbon-like curved shape, composed of metal or other suitable material, attached either to a central axle, or alternatively to the inner surface of a cylinder or cone revolving within a tube-like space. Two or more parallel ribbon drives may be required within each cylinder or cone, to maximize balance and to minimize vibrations of a ribbon drive unit. Additionally, it is preferrable to employ the drives in conter-rotating pairs so as to cancel torsional forces on the vessel.
A key element of both the central and peripheral designs of the ribbon drive is that there is a change in the frequency of curves of the ribbon drive, which proceeds from a high frequency (i.e. many coils per unit length) to a low frequency of coils per unit length with an associatated decrease in helix angle of the ribbon-like band when viewed lateral to the axis. For example, in lateral appearance, the ribbon drive would present a tight curved helix angle, which would be nearly perpendicular to the axial flow of water entering the ribbon drive, changing/progressing rearward to a more gradual curve at a helix angle of approximately 30 degrees to the axis, although this is not meant as a limitation since other angles may also prove beneficial.
The initial tight curves of the ribbon drive draws in fluid, such as water, from all directions in front of the intake. This water has initial velocities with high radial/circumferencial components and an initial axial component. The rotating ribbon drive imparts forces on the water and the decreasing frequency of the ribbon drive changes both the direction of the applied force and the resulting water velocity. The result is a higher axial velocity component for the water at the outlet, thereby increasing the axial component of momentum in order to drive the vehicle in an axial direction.
Assume that a fluid, such as water, is moving along at a rate of speed xe2x80x9ca.xe2x80x9d Initial energy is imparted to water moving along the central linear axis of the ribbon drive by a high frequency coil. The amount of energy depends upon the revolutions per minute (R.P.M.) of the central linear shaft and thus of each coil of the helical shape. A unit of water upon exiting coil HF#1 (high frequency, 1st coil) is moving at velocity xe2x80x9ca+1. xe2x80x9d If a second, identical subsequent coil HF#2 is turning at the same rate as HF#1, then it too,can only add xe2x80x9c1xe2x80x9d to initial velocity xe2x80x9caxe2x80x9dxe2x80x94not xe2x80x9c1xe2x80x9d to xe2x80x9ca+1xe2x80x9dxe2x80x94because HF#2 and HF#1 would be rotating at the same speed. Further, having the same helix angle at HF#2 would even act to impede the rapid passage of water moving at xe2x80x9ca+1xe2x80x9d having exited from HF#1, rather than to facilitate the water passage with a less steep helix angle. Increasing the frequency of HF-#2 (making it a tighter coil, with a steeper helix angle) would make it act more like a wall than a water conduit, while rotating on the same shaft as HF#1 . Therefore, the coil at an HF#2 position, rotating on the same shaft and at the same RPM as HF#1, must be a coil of lower frequency than HF#1, said second coil now called MF#1 (1st middle frequency coil).
A unit of energy initiated at the front edge of HF#1, by the rotation of the ribbon drive, is transferred to move water along the edge of its relatively vertical ribbon-like band/vane, with a small net increase in the axial velocity. The unit of energy next reaches MF#1 coil, moving along the edge of the more spread-out coil of the vane, traveling a greater distance along the edge of the vane in MF#1 compared to HF#1 per rotation. Therefore the unit of energy travels faster axially since a 360 degree curve of the MF#1 coil is more spaced out, stretched out as it were, along the central axle.
The unit of energy is imparted to unit volumes of water (for discussion purposes) moving rearward through the ribbon drive. The energy is applied at a constant rate (all coils turning at the same RPM) but along a constantly longer path. That longer path accommodates the unit of water moving at xe2x80x9ca+1xe2x80x9d because the vane face is less vertical than at HF#1, the vane edge is less vertical/more horizontal in MF#1 (the second coil in a ribbon drive propulsion system), with the unit of energy moving faster axially. Similar reasoning applies to the subsequent low frequency curve LF#1, the final curve or coil in a 3-coil setup.
Considereing a unit volume of water exiting from HF#1 at velocity xe2x80x9ca+1,xe2x80x9d it is then exposed to additional rotating coil faces which must be less angled to accommodate the increased velocity imparted by HF#1. The result is that energy is increasingly imparted to an initial volume of fluid as it moves rearward in the ribbon drive propulsion tube at an ever increasing axial velocity.
Since water is contained within the cylinder of a ribbon drive propulsion system, its velocity through the cylinder (rotating at a constant R.P.M.) should progressively increase, with the volume exiting the rear being limited by the net water intake in the forward half, and the diameter of the exit outlet. Negative internal pressures found to be present (experimentally) in the forward half tend to support the theory of increasing velocity along the ribbon drive unit interior.
Coil frequencies and axial lengths can be optimized. Coils, divided into separate sections and arranged in series, can also be rotated at different RPM""s (by separate drive means) to achieve optimal output. The lead HF#1 coil can be designed to fold away from the water path, such as by the iris-fan embodiment discussed below.
As noted above, there are two general embodiments of the ribbon drive propulsion system of the present invention. The first alternative embodiment is the central design concept. The central design is generally helical and looks similar to a corkscrew, but significantly different, having an increasingly stretched out frequency of coils (i.e., an increasing screw pitch). The band-like surface of the ribbon shape forces water to be angled rearward and outward from the central linear axle. Since the central linear axle operates within a propulsion tube, the water is contained and forced backward to propel the vessel (e.g. surface vessel or submarine) forward.
In practice, the band-like surface of the ribbon is preferably cupped, to provide an inward angle for the band-like ribbon surface. This helps limit the centrifugal effect of the ribbon drive, which tends to impel water outward toward the wall of the cylindrical tube in which the central linear axle is located. In addition, this cupped ribbon surface directs water more in a rearward direction, with less water angled off the ribbon material to the walls of the propulsion tube.
To assist in preventing cavitation of the water, slipstream inlet channels can be added in the low pressure regions. Since water is not compressible, the ribbon drive propulsion system does not pretend to compress the water, but rather to hasten its exit rearward by not impeding further rearward flow while simultaneously adding more xe2x80x9cpushxe2x80x9d from the decreasing frequency design of the vane coils. Further, the converse of compression is expansion, which water cannot do, either. Because water does not expand at the side of a propeller blade that is pushing/corkscrewing water toward the rear, air bubbles tend to form in the areas where there is decreased or negative pressure due to water being accelerated rearward, creating a shear within the water.
Slipstream channels will help prevent such cavitation by providing additional water (ducted from the outer surface of the hull or propulsion tube) to that area in the drive stream where negative pressure exists immediately rearward of the first coil turn in the ribbon drive. The slipstream channels thus may provide the following advantages, particularly in a ribbon-drive propulsion system type of model: decreased bubble formation or cavitation, increased volume of water ejected rearward/increased thrust, and possibly improved water flow at the hull surface boundary layer.
In the second alternative embodiment, the ribbon-like band is attached peripherally to the inside surface of a propulsion tube or of a series of peripheral rings. In this instance, the entire cylinder rotates, and the coils of the ribbon band on the periphery of the interior of the tube cause water to be angled rearward, as well as toward the center, i.e. the central linear axis, of the cylindrical tube. The ribbon-like band attached to the periphery of the inside of the propulsion tube of the peripheral design may be a single continuous ribbon-like band. Alternatively, the first coil (HF#1) of the xe2x80x9cbandxe2x80x9d may be an xe2x80x9ciris-fanxe2x80x9d formed by a series of rotatable blades all in one plane at the intake end of the cylinder. Each blade may be xe2x80x9cfeatheredxe2x80x9d or angled to adjust the angle of attack. These blades may also be radially retractable with respect to the cylinder to varying degrees (like the iris of a camera) in order to maximize the velocity of the water being propelled through the cylinder, and once thay have initiated water movement rearward through the ribbon drive, these blades can be completely retracted from the water channel and their rotation stopped.